1. Field of the Invention
This invention relates to hardware fittings and more particularly to stays for the adjustable mounting of window sashes in window frames.
2. Discussion of the Background
A projected hung window sash is one which is mounted in a fixed window frame by at least a pair of stays. The window sash can be side hung with the stays situated at the top and bottom of the sash or it can be top hung with the stays located nearer the top edge of the sash. The sash is coupled to the frame via arms which conventionally are pivotally attached to mounting plates which themselves are fastened to the sash and frame. A well known form of window stay incorporates a pair of unequal length arms pivotally mounted at each end to frame and sash mounting plates. Such a stay is often referred to as a four bar stay. It is also known to provide six bar stays which are essentially a four bar stay with the inclusion of two additional arms. It is further known to provide such stays with one or more of the pivot points being slidable during all or part of the opening and closing of the stay.
Irrespective of their design or geometric configurations stays for projected hung windows provide a certain amount of "pull-in" at the final stages of closing of the sash. This pull-in effectively constitutes, relative to the plane of the frame, a sideways or transverse movement or component of movement so that not only is the portion of the sash opposite to that which will be internally latched moved into a fully closed position in the frame but usually ensures that weather seals with the frame or sash are compressed so as to provide an overall seal between the sash and frame. This pull-in can be provided by the actual geometry of the stay, by a sliding movement of one or more pivots or by a fixed guide with which part of the stay engages and imparts the sideways movement or component of movement.
Standards specification usually require that projected hung windows be able to resist opening in the event of negative pressures. This resistance to opening is in part provided by the internal latching of the sash (e.g. by a wedge lock), however, it is primarily the action of the stays which prevent that portion of the window sash opposite to which the internal fastening is attached from being sucked open.
In addition it is usually very difficult to provide a stay construction which achieves pull-in movement over the whole of the sash sufficient to ensure that entire compression of the weather seal takes place.
The aforementioned requirements and the difficulties associated with some stay constructions are compounded by present day demands that stays be able to fit within confined (more particularly narrow) cavities between the sash and frame.